Eldorado Collection:http://hdl.handle.net/2003/411892024-03-29T02:39:46Z2024-03-29T02:39:46ZEnhancing electron correlation at a 3d ferromagnetic surfaceJanas, David MaximilianDroghetti, AndreaPonzoni, StefanoCojocariu, IuliaJugovac, MatteoFeyer, VitaliyRadonjić, Miloš M.Rungger, IvanChioncel, LiviuZamborlini, GiovanniCinchetti, Mirkohttp://hdl.handle.net/2003/422622024-01-05T23:12:29Z2022-10-27T00:00:00ZTitle: Enhancing electron correlation at a 3d ferromagnetic surface
Authors: Janas, David Maximilian; Droghetti, Andrea; Ponzoni, Stefano; Cojocariu, Iulia; Jugovac, Matteo; Feyer, Vitaliy; Radonjić, Miloš M.; Rungger, Ivan; Chioncel, Liviu; Zamborlini, Giovanni; Cinchetti, Mirko
Abstract: Spin-resolved momentum microscopy and theoretical calculations are combined beyond the one-electron approximation to unveil the spin-dependent electronic structure of the interface formed between iron (Fe) and an ordered oxygen (O) atomic layer, and an adsorbate-induced enhancement of electronic correlations is found. It is demonstrated that this enhancement is responsible for a drastic narrowing of the Fe d-bands close to the Fermi energy (EF) and a reduction of the exchange splitting, which is not accounted for in the Stoner picture of ferromagnetism. In addition, correlation leads to a significant spin-dependent broadening of the electronic bands at higher binding energies and their merging with satellite features, which are manifestations of a pure many-electron behavior. Overall, adatom adsorption can be used to vary the material parameters of transition metal surfaces to access different intermediate electronic correlated regimes, which will otherwise not be accessible. The results show that the concepts developed to understand the physics and chemistry of adsorbate–metal interfaces, relevant for a variety of research areas, from spintronics to catalysis, need to be reconsidered with many-particle effects being of utmost importance. These may affect chemisorption energy, spin transport, magnetic order, and even play a key role in the emergence of ferromagnetism at interfaces between non-magnetic systems.2022-10-27T00:00:00ZUltrafast coherent THz lattice dynamics coupled to spins in the van der Waals antiferromagnet FePS3Mertens, FabianMönkebüscher, DavidParlak, UmutBoix-Constant, CarlaMañas-Valero, SamuelMatzer, MargheritaAdhikari, RajdeepBonanni, AlbertaCoronado, EugenioKalashnikova, Alexandra M.Bossini, DavideCinchetti, Mirkohttp://hdl.handle.net/2003/421652023-10-20T22:12:28Z2022-12-21T00:00:00ZTitle: Ultrafast coherent THz lattice dynamics coupled to spins in the van der Waals antiferromagnet FePS3
Authors: Mertens, Fabian; Mönkebüscher, David; Parlak, Umut; Boix-Constant, Carla; Mañas-Valero, Samuel; Matzer, Margherita; Adhikari, Rajdeep; Bonanni, Alberta; Coronado, Eugenio; Kalashnikova, Alexandra M.; Bossini, Davide; Cinchetti, Mirko
Abstract: Coherent THz optical lattice and hybridized phonon–magnon modes are triggered by femtosecond laser pulses in the antiferromagnetic van der Waals semiconductor FePS3. The laser-driven lattice and spin dynamics are investigated in a bulk crystal as well as in a 380 nm-thick exfoliated flake as a function of the excitation photon energy, sample temperature and applied magnetic field. The pump-probe magneto-optical measurements reveal that the amplitude of a coherent phonon mode oscillating at 3.2 THz decreases as the sample is heated up to the Néel temperature. This signal eventually vanishes as the phase transition to the paramagnetic phase occurs, thus revealing its connection to the long-range magnetic order. In the presence of an external magnetic field, the optically triggered 3.2 THz phonon hybridizes with a magnon mode, which is utilized to excite the hybridized phonon–magnon mode optically. These findings open a pathway toward the optical control of coherent THz photo–magnonic dynamics in a van der Waals antiferromagnet, which can be scaled down to the 2D limit.2022-12-21T00:00:00ZPhononkopplung an Spins und Ladungen auf der ultraschnellen Zeitskala im antiferromagnetischen Halbleiter MnTeTerschanski, Marchttp://hdl.handle.net/2003/411992023-01-18T23:12:28Z2022-01-01T00:00:00ZTitle: Phononkopplung an Spins und Ladungen auf der ultraschnellen Zeitskala im antiferromagnetischen Halbleiter MnTe
Authors: Terschanski, Marc
Abstract: Im ersten Teil dieser Arbeit wird ein neu installierter Aufbau beschrieben, der die gleichzeitige Durchführung optischer und magneto-optischer Pump-Probe Experimente als Funktion der Temperatur, eines Magnetfeldes oder eines angelegten elektrischen Feldes ermöglicht. Im zweiten Teil dieser Arbeit wird mit optischen Anregungen untersucht, ob eine Kopplung zwischen dem Spinsystem und dem elektronischen System in dem magnetischen Halbleiter α-MnTe existiert. Dazu wird eine 200 nm dicke Schicht α-MnTe mit verschiedenen experimentellen Methoden vermessen. Die Bandlücke von α-MnTe ist um einen zusätzlichen Beitrag in der antiferromagnetischen Phase blauverschoben, welcher proportional mit der Untergittermagnetisierung skaliert. Diese statische Kopplung zwischen der Bandlücke und dem Spinsystem wird erfolgreich in unserer Probe reproduziert. Darauf aufbauend wird die Dynamik der Bandlücke unter Verwendung des Pump-Probe Verfahrens untersucht. Die transiente Reflektivität zeigt, dass die Bandlücke durch das optisch aktive α-Phonon kohärent moduliert wird. Im finalen Schritt wird die Bandlücke kohärent angeregt und die Antwort des Spinsystems, die Rotation der Polarisation, detektiert. Diese ist ebenfalls durch das α-Phonon kohärent moduliert und zeigt einen zusätzlichen inkohärenten Beitrag in der antiferromagnetischen Phase, welcher eindeutig auf die magnetische Ordnung zurückzuführen ist. Die Zerfallszeit dieses Beitrags entspricht der der Zeitskala der Untergitterdemagnetisierung. Somit konnte in dieser Arbeit eine phonongestützte Kopplung zwischen dem elektronischen System und dem Spinsystem in α-MnTe gezeigt werden.; In the first part of this thesis, a newly constructed set-up is described that allows simultaneous optical and magneto-optical pump-probe experiments to be performed as a function of temperature, magnetic field or an applied electric field. In the second part of this work, optical methods are used to investigate whether a coupling exists between the spin system and the electronic system in the magnetic semiconductor α-MnTe. For this purpose, a 200 nm thick layer of α-MnTe is measured with different experimental methods. The band gap of α-MnTe experiences an additional blue shift in the antiferromagnetic phase, which scales proportionally with the sublattice magnetisation. This static coupling between the band gap and the spin system is successfully reproduced in our sample. Based on this, the dynamics of the band gap is investigated using the pump-probe method. The transient reflectivity shows that the band gap is coherently modulated by optical active α-phonons. In the final step, the band gap is coherently excited and the response of the spin system, the rotation of the polarisation, is detected. Again the rotation of polarisation is coherently modulated by the α-phonon and shows an additional incoherent contribution in the antiferromagnetic phase, which is ascribed to the magnetic order. The decay time of this contribution corresponds to the time scale of the sublattice demagnetisation. Thus, a phonon-assisted coupling between the electronic system and the spin system on the femtosecond timescale in α-MnTe has been demonstrated in this work.2022-01-01T00:00:00Z